Characterization and retroviral transduction of an early human lymphomyeloid precursor assayed in nonswitched long-term culture on murine stroma

In the hierarchy of human hematopoietic progenitors, longterm culture-initi ating cells (LTC-IC) and extended LTC-IC belong to the earliest cell popula tions that can be assayed in vitro. We report the identification of a multi potential lymphomyeloid progenitor detected in a nonswitch culture system. We observed the emergence of CD33(+) myeloid and CD19(+) B-lymphoid cells f ollowing plating of lineage-depleted (Lin(-)) CD34(+)-enriched or purified CD34(+)CD38(-) cord blood cells on MS-5 stroma in the absence of exogenous cytokines, Both CD19(+)CD20(-) pro-B and CD19(+)CD20(+) pre-B lymphocytes c oexist with myeloid cells in long-term culture. A limiting dilution approac h was used to show that a single CD34(+)CD38(-) cell can generate lymphomye loid progeny in conventional (5-week) and extended (10-week) cultures. Most of the clones in longterm culture or extended long-term culture contained not only lymphoid and myeloid cells, but also myeloid clonogenic progenitor s. A high proportion of CD34+CD38- cells gave rise to lymphomyeloid clones after 5 and 10 weeks of culturing (up to 48% and 16%, respectively), which distinguishes the assay reported here from those using switch culture condi tions. We performed retroviral gene transfer experiments involving 1-3 days of exposure of Lin(-)CD34(+)-enriched cells to virus encoding enhanced gre en fluorescent protein, Monitoring of gene transfer efficiency into LTC-IC by enhanced green fluorescent protein fluorescence showed that it is possib le to achieve marking of lymphomyeloid LTC-IC, albeit to a lesser extent th an myeloid-restricted LTC-IC, (C) 1999 International Society for Experiment al Hematology. Published by Elsevier Science Inc.